Environmental factors are more easily manipulated than genes but that's far from saying it's easily done. In fact, it's almost impossible. If your parents are overweight, illiterate, morons who've never worked in their lives, and all their friends are similar, which is likely, then YOU ARE TOAST.
All that is assuming your interpretation of heritability is correct. I don't think it is...but it'd take quite a bit of research to be sure. I'll give you a hint as to why I think you're wrong. The IQ distribution curve is bell shaped, not linear.
It is not my interpretation, it is based upon numerous studies, and you said you agreed with it until I explained what it actually meant to you.
So if you made it an average black kid instead of a white kid then of the 20 IQ point difference 12 points would be due to environment and 8 points would be genetic. If you raised that kid in an “Asian” environment his IQ would be 102 (higher than average), while if you somehow gave him Asian genetics his IQ would only be 98 (slightly below average).
Height distribution is also bell shaped not linear. The distribution of almost any quantifiable trait is bell shaped not linear. This has nothing to do with if it has a genetic or environmental cause or causes.